It is known to control the timing of an ignition event in external ignition internal combustion (IC) engines in dependence on operating or operation or environmental parameters. Typical operating parameters are engine speed, loading, temperature, deflection angle of the throttle, whether the engine is under starting conditions or not, and also exhaust gas composition. In one such systems which operates digitally, temporally sequential signal trains are accumulated in an accumulator counter until the counter reaches a predetermined value. One of the signal trains is derived from a memory which is addressed in dependence on the external operating parameter by an address counter. When the accumulator has reached a predetermined count state, which can be determined by comparison with a suitable decoder or matrix, the ignition event is triggered, for example by controlling opening of a switch in the primary of an ignition coil, thus inducing at least the first one of a spark flash-over at a spark plug.
IC engines can be operated with fuel-air mixtures supplied either by a carburetor or by a fuel injection system, in which typically an electronic fuel injection system is provided. The amount of fuel being injected can be controlled in dependence on exhaust gas composition, to optimize the composition of the exhaust gases in the sense that they provide a minimum of noxious components. Fuel injection systems of this type are usually controlled by an oxygen sensor located in the exhaust pipe or exhaust channel from the IC engine, operating as a .lambda. sensor in form of a .lambda. control. Carburetors, also, can be adjusted, for example by an electromagnetic positioning element to vary the through-put of fuel with given throttle positions in dependence on exhaust gas composition. Changing the operating characteristics of a carburetor is much nore difficult, however, then changing the operating conditions of an electronically controlled fuel injection system.
It is well known that ignition timing has a definite effect on the operating characteristics of an IC engine, and it is also known that ignition timing has an effect on the exhaust gas compositon from the engine.